1. Field of the Invention
The present invention relates to an image processing apparatus and image processing method, which generate a composite image obtained by embedding additional sub information such as security information, which is different from a main image, into the main image such as a face image of a person, an image printed on a recording medium, and a print product on which a composite image generated by the image processing apparatus or image processing method is printed.
2. Description of the Related Art
In recent years, various security techniques are applied to ID cards (personal authentication media) such as various licenses, credit cards, membership cards, and the like.
As one security technique (first security technique) to be applied to such ID cards, for example, Japanese Patent No. 2,840,825 describes a technique for forming a hologram film on an image display medium (recording medium) to attain copy protection.
As another security technique (second security technique) to be applied to the ID cards, a digital watermark technique is known. This digital watermark technique is a technique for generating a composite image by embedding additional sub information into a main image. Such digital watermark technique is used as the security technique for preventing counterfeiting, falsification, or the like ID cards. For example, the digital watermark technique is applied to an image such as a face image printed on each ID card.
Furthermore, as the above digital watermark technique, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-248935 discloses a technique for embedding sub information which is invisible to the human eye into a to-be-embedded image (main image) by exploiting high spatial frequency components and color difference components which are not perceptible by the human. Also, Jpn. Pat. Appln. KOKAI Publication No. 11-355554 discloses a technique for varying the embedding strength of a digital watermark depending on the contents of a to-be-embedded image (main image). Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 2001-268346 discloses a printing apparatus used to print, on a recording medium, a composite image in a state wherein sub information is visible to the human eye using an optical filter.
However, when a hologram film is further formed on a recording medium on which a composite image generated by the digital watermark technique is printed, an optical scanning device such as a scanner, camera, or the like can hardly scan an image of a region where the hologram film is formed of the composite image printed on the recording medium. For this reason, when the hologram film is formed on the recording medium on which the composite image is printed, it becomes difficult to reconstruct sub information embedded in the composite image which is printed on the recording medium.